You could try to enable a high pass filter at around 30 Hz (per your bass cab specs) and lowering the limiter threshold. Try it one dB at a time, starting at -1 dB.

What is the current position of the input attenuator? Do your input signal in SA is below clip?

As mentioned above (and below), I have a HP set in at 35hz. The input signal in SA is close to 0db (generally between 0db and -10db) though even if it looks at though it has spiked above 0db I am totally unable to make the clip indicator on the input stage light within SA regardless of what is thrown at it.

The power amp attenuator was at 3o'clock. The Pre amp output volume was VERY LOW (around 9 o'clock) in order to keep the input gain low right.

QUOTE(dakos @ Feb 16 2012, 06:18 AM)

He already has a HP filter and the older XTIs only have -3dB, -6dB and -12dB settings...The sound you hear is the thermal limiter engaging, it was described by many as "shattered glass"...Take a little load of the amp or adjust the fans to "full speed" setting, see which works better for you.

Thermal clipping - interesting. I see no mention of that in the manual. Though the shattering of glass may be a suitable description - will this harm my speakers? It was only triggered by a handful of notes and all on the high C string (I play 6 string bass) when using an octave pedal (to reproduce the note 1 octave lower - so still 'high' for a bass note). These notes are Audibly more resonant due to the way the octave pedal tracks higher pitches so I'll try and avoid them! Lol. When you say 'take a little load off', I assume you mean back off the power amps attenuator rather than the preamp signal? Fan - as in always on? (I see no way to select a fans speed, just at what temperature it kicks in, or to leave it on constant). The fan is fine for live work I find, but in the studio it seems so LOUD it almost off putting

Sorry about spreading bad information about the limiter! I was going by my general understanding of how a DSP works, but have not used XTi amps in particular.

Anyway, the thermal led or circuit activating on peaks seems like an abnormal behavior. Overheating in an amps usually develops over an extended period, not on a sudden peak. Then, protection circuitery should kick in and protect the amp and the intergity of the signal in a gracefull way, while the overload occurs. Producing spurious sounds at the output is not normal and is not acceptable in a device meant to be used professionnally in front of an audience, imho.

Unless the thermal led on the XTi is also a general fault indicator...

Sorry about spreading bad information about the limiter! I was going by my general understanding of how a DSP works, but have not used XTi amps in particular.

Anyway, the thermal led or circuit activating on peaks seems like an abnormal behavior. Overheating in an amps usually develops over an extended period, not on a sudden peak. Then, protection circuitery should kick in and protect the amp and the intergity of the signal in a gracefull way, while the overload occurs. Producing spurious sounds at the output is not normal and is not acceptable in a device meant to be used professionnally in front of an audience, imho.

Unless the thermal led on the XTi is also a general fault indicator...

This was also my understanding. The manual explains it in a fairly 'regular' way. The clip light is for clipping and the thermal light comes on to indicate overheating, at which point the output stops. It also comes on to show certain faults in combination with other lights. It seemed to be coming on as described just before the clipping point... Which is why I thought it was acting as an indicator for the limiter cutting in (at -3db/jut under clip). I was wondering if there was an option in SA that I had activated to show the limiters status on the front panel.

Sorry about spreading bad information about the limiter! I was going by my general understanding of how a DSP works, but have not used XTi amps in particular.

Anyway, the thermal led or circuit activating on peaks seems like an abnormal behavior. Overheating in an amps usually develops over an extended period, not on a sudden peak. Then, protection circuitery should kick in and protect the amp and the intergity of the signal in a gracefull way, while the overload occurs. Producing spurious sounds at the output is not normal and is not acceptable in a device meant to be used professionnally in front of an audience, imho.

Unless the thermal led on the XTi is also a general fault indicator...

This ungraceful limiter operation is defiantly one of the problems the older XTIs had and they are pretty well known for it. This behavior is one of the reasons why the XTI family is not considered a good amp for sub (or bass) duty.

This ungraceful limiter operation is defiantly one of the problems the older XTIs had and they are pretty well known for it. This behavior is one of the reasons why the XTI family is not considered a good amp for sub (or bass) duty.

Annoyingly, the reason I went for the XTi was due to a large number of highly positive pieces of feedback from bassists regarding the amp and it's useful DSP and uncoloured sound. Feeling a little frustrated by it all.

This ungraceful limiter operation is defiantly one of the problems the older XTIs had and they are pretty well known for it. This behavior is one of the reasons why the XTI family is not considered a good amp for sub (or bass) duty.

Annoyingly, the reason I went for the XTi was due to a large number of highly positive pieces of feedback from bassists regarding the amp and it's useful DSP and uncoloured sound. Feeling a little frustrated by it all.

All I can say is... welcome to pro audio.Every profesional tool has its advantages and disadvantages, knowing what they are should make you a more educated user, don't be frustrated. You have a great tool at hand, it just needs you to use it within its operational bounderies.

A few suggestions and questions:One thing I see you're doing a bit wrong is your HP filter setting, it should be set at the -3dB point of your speaker, not your -10dB. So set your HP filter to 44Hz with Butterworth 24db/Oct slope, this should draw less current from your amp that's being wasted as heat and not hurt the SQ. Note that this is the recomended initial setting, this is not an absolute number and it should be tweaked in accordance with your musical needs.

Also after looking at your speaker, I see you are running the amp bridged @4 ohm, this is an extreme load for any amp, especially on sub duty, especially when you further push it with the +3dB EQ setting @50Hz and those octave pedals. This type of load will put almost every amp into thermal especially budget amps.

Sone things that would help us further figure out if there are additional problems that contribute to this thermal limiting... Do you have the amp inside a rack? Is there something blocking the air passage? Is your grid voltage stable?

I was confused about the fan setting it exists on the newer XTIs (1002, 2002, 4002, 6002) and not the older ones (1000, 2000, 4000, 6000).

The thermal limiter will not hurt your speakers.

It sounds like your amp gain and preamp gain are set up properly, do you hear an upgrade in volume?

How you back off is of no consequence, on the pre, on the amp or on the octave pedal, all should get the job done.

A few suggestions and questions:One thing I see you're doing a bit wrong is your HP filter setting, it should be set at the -3dB point of your speaker, not your -10dB. So set your HP filter to 44Hz with Butterworth 24db/Oct slope, this should draw less current from your amp that's being wasted as heat and not hurt the SQ. Note that this is the recomended initial setting, this is not an absolute number and it should be tweaked in accordance with your musical needs.

Cool. 35hz was an initial suggestion from the cab manufacturer. My sound is very full range, hence choosing a cab with a tweeter, but as I play live drum & bass, my core 'bass' tone is a little more sub than a typical live bass player. I guess I should start letting the club PA's do a little more work for me! I shall make this change when I'm at the studio over the weekend and see how it sounds.

QUOTE(dakos @ Feb 16 2012, 05:24 PM)

Also after looking at your speaker, I see you are running the amp bridged @4 ohm, this is an extreme load for any amp, especially on sub duty, especially when you further push it with the +3dB EQ setting @50Hz and those octave pedals. This type of load will put almost every amp into thermal especially budget amps.

I have since removed the output EQ boost (before the thermal clipping happened yesterday) due to the realisation that any DI taken at live shows is from the Preamp and that boosting at the power amp stage is only going to give me a sound in the studio/from the cab that is not reproduced through a venue PA. therefore that is no longer an issue (but was not adding to the cause of yesterdays issues). As for the bridge mono mode - the amp was bought to provide me that amount of headroom. As 'powerful' bass amps were being pushed to audible distortion at the output due to EQ'ing in lower bass frequencies. This allowed me more headroom for doing so. As you point out though - maybe its not the 'best' amp for the job.

QUOTE(dakos @ Feb 16 2012, 05:24 PM)

Sone things that would help us further figure out if there are additional problems that contribute to this thermal limiting... Do you have the amp inside a rack? Is there something blocking the air passage? Is your grid voltage stable?

Yes the amp is in a 3U Gator shallow rack. The amp is literally exactly the same depth as the rack so the back (and the fan) poke out just a bit, meaning the air flow goes straight out into the room behind it. It has the preamp above it in the rack, which runs constantly cold and doesn't add any additional heat to the racks airflow. Voltage wise, it's an oldish building in a city centre so I'd say it was far from stable. Most venues I've played recently have been far worse though (one even put some of my effects pedals into crazy shutdown). I don't experience any issues in terms of mains hum etc within our studio though.

QUOTE(dakos @ Feb 16 2012, 05:24 PM)

I was confused about the fan setting it exists on the newer XTIs (1002, 2002, 4002, 6002) and not the older ones (1000, 2000, 4000, 6000).

The thermal limiter will not hurt your speakers.

It sounds like your amp gain and preamp gain are set up properly, do you hear an upgrade in volume?

How you back off is of no consequence, on the pre, on the amp or on the octave pedal, all should get the job done.

Cool. The output gain will increase and decrease along with the XTi's attenuator though if I am correct? Whereas the input gain (seen in SA and is not clipping) will reduce with the output of the preamp before it?

So the immediate problem is fixed for now. However, this 44 Hz filter means you are not reproducing several of the lowest notes, moreso on a 6 strings. IMHO, you should continue to investigate the original issue and resume operation with a lower high pass filter frequency.

So the immediate problem is fixed for now. However, this 44 Hz filter means you are not reproducing several of the lowest notes, moreso on a 6 strings. IMHO, you should continue to investigate the original issue and resume operation with a lower high pass filter frequency.

Due to the natural frequency response of the speaker he is not reproducing these tones anyway so why waste all the energy and put the amp into thermal?

So the immediate problem is fixed for now. However, this 44 Hz filter means you are not reproducing several of the lowest notes, moreso on a 6 strings. IMHO, you should continue to investigate the original issue and resume operation with a lower high pass filter frequency.

There is a noticeable change in the floor moving low frequencies, but then the club PA will do a large portion of these for me. Also, not hearing the fundamental of a low B is something that most bass players are used to. Very few amp and cab combos will do so efficiently. I agree though, IF there was another way around it then it's certainly something I'd investigate.

QUOTE(dakos @ Feb 21 2012, 04:55 AM)

Due to the natural frequency response of the speaker he is not reproducing these tones anyway so why waste all the energy and put the amp into thermal?

My thinking too.

A friend has lent me a new Genz Benz Streamliner 900 bass amp fo me to play with. I 'll be interested in how it stacks up against the pre and power set up. at 900w into 4 Ohms I'm very interested to check out these new super high power mini amps.